Win McNamee/Getty ImagesU.S. Defence Secretary Jim Mattis listens as U.S. President Donald Trump answers questions during a meeting with military leaders in the Cabinet Room on October 23, 2018 in Washington, DC.

Outgoing Defence Secretary Jim Mattis was a buffer between President Donald Trump and the most powerful military on earth.

Now that buffer is gone and may never come back.

Mattis reportedly slow-walked Trump policies in an apparent attempt to appease the president while reassuring allies and managing the military.

But now a new Defence Secretary may find themselves working to ban transgender service, build a border wall, or even exit NATO.

Outgoing Defence Secretary Jim Mattis served as a buffer between the impulses of President Donald Trump and the actions of the most powerful military on earth.

But now that buffer is gone, and may never come back.

Mattis quit on Thursday, citing Trump’s lack of demonstrated respect for US allies and his ambiguous approach to adversarial nations like China and Russia.

He wrote to Trump that he had “the right to have a Secretary of Defence whose views are better aligned with yours on these and other subjects.”

Mattis was the last remaining “adult in the room,” a term used by US allies to describe a team of respected professionals in Trump’s cabinet. In his role he routinely responded to snap-decisions Trump announced on Twitter, and was tasked with making them a reality.

This includes Trump’s decision to ban transgender US citizens from serving in the military, his announcement that the US would suspend military exercises with South Korea, and the decision to deploy US troops to the southern border with Mexico.

But, rather than continue to serve as this buffer, Mattis threw in the towel on Thursday after Trump broke with him in announcing a withdrawal from Syria and reportedly a partial withdrawal from Afghanistan.

Instead, Mattis called for a Defence Secretary who would do Trump’s bidding.

Here are a few tasks a Defence Secretary better-aligned with Trump may find themselves doing: